Reed switch matrix with high frequency transmission capability

ABSTRACT

A strip-line crossbar switch with reed switches at the crosspoints and optional magnetic latching, especially suitable for switching signals at frequencies of up to several tens of megahertz. Magnetic fields for actuating the reed switches are applied transversely across, and highly concentrated at the contact points. The actuating fields are generated by coils wound on magnetic cores, and are directed to the reed switches by pole pieces, which extend along and on opposite sides of the reed switches, and also function as magnetic shields to reduce magnetic coupling between adjacent cross-points.

United States Patent [72] lnventors Larry L. Lnunt Holcomb; Gary E. Northrup, Rochester, both of, N.Y. [21] Appl. No. 839,479 ['22] Filed July 7, 1969 [45] Patented June 1,1971 [73] Assignee Cunningham Corporation Honeoye Falls, N.Y.

[54] REED SWITCH MATRIX WITH HIGH FREQUENCY TRANSMISSION CAPABILITY 3 Claims, 4 Drawing Figs.

[52] US. Cl. 335/112 [51] Int. Cl. H0lh 67/30 [50] Field o1Search....; 335/151, 152, 153, 154, 1 12; 333/84 M [56] References Cited UNITED STATES PATENTS 3,002,066 9/1961 Ketchledge 335/152 3,454,911 7/1969 Rouzier 335/112 3,500,267 3/1970 Wasserman 335/112 3,508,] 80 4/1970 Mayer 335/152 Primary Examiner-Harold Broome Attorneys-Hoffman Stone and Morton A. Polster ABSTRACT: A strip-line crossbar switch with reed switches at the cross-points and optional magnetic latching, especially suitable for switching signals at frequencies of up to several tens of megahertz. Magnetic fields for actuating the reed switches are applied transversely across, and highly concentrated at the contact points. The actuating fields are generated by coils wound on magnetic cores, and are directed to the reed switches by pole pieces, which extend along and on opposite sides of the reed switches, and also function as magnetic shields to reduce magnetic coupling between adjacent crosspoints.

PATENTEUJUN n91: 3,582,844

SHEETIUFZ INVENTOR. LARRY L. LAUNT BY GARY E. NZSTHRUP ATTORNEY PATENTED JUN 1 |97| SHEET 2 [IF 2 4 INVENTOR. LARRY L. LAUNT BY GARY E. NORTHRUP ATTORNEY REED SWITCH MATRIX WITH HIGH FREQUENCY TRANSMISSION CAPABILITY BRIEF SUMMARY This invention relates to a novel crossbar switch arrangement including reed switches, capable of handling signals of relatively high frequency, and with inherently low magnetic coupling between cross-points,

Crossbar switches of many different types have been proposed, and several types are in widespread use. Heretofore, most crossbar switches have been limited in respect of the frequency of signals that they could handle without excessive cross talk and degradation. Reed switches, commonly hermetically sealed in glass envelopes, have also been proposed for use in crossbar switches, but their use has encountered problems relating primarily to magnetic coupling among different cross-points, resulting at times in the undesired closing of switches in response to actuation of other, nearby switches. This has required the use of special magnetic shielding in some instances, or the provision of relatively large spacings between adjacent cross-points. In the former case, construction is complicated and expense increased. ln the latter case, the crossbar switch must be made larger than desired for a given capacity.

The crossbar switch of the present invention resolves these problems to a high degree. It is capable of handling signals at several lOs of megahertz with very low crosstalk and signal degradation. It also may be made very compact without the need for special magnetic shielding and without danger of switch actuation by cross coupling.

Briefly, the crossbar switch of the invention includes coordinate, crossed conductor arrays arranged on printed circuit cards according to strip-line techniques for the efficient transmission of signals of high frequencies. Connections between the conductors are made by reed switches mounted at the respective cross-points. The reed switches are actuated by energizing coils mounted on magnetic cores. Pole pieces extend from the cores along opposite sides of the reed switches, both to concentrate the magnetic flux at the contact points of the reed switches and to shield the reed switches from stray magnetic fields. The arrangement may be characterized by the direction of the actuating magnetic field relative to the length of the reed switches. In the arrangement of the invention, the actuating field is applied transversely across the reed switches and highly concentrated in the region of their contact points. This contrasts with the usual arrangement of the prior art wherein the actuating flux is applied to extend lengthwise of the reed switches.

In the preferred form of the invention, the cores are of a hard magnetic material, as described in the copending application of Conklin and lmes, Ser. No. 809,301, filed Mar. 21, l969, entitled Magnetically Latchable Reed Relay" and assigned to the present assignee now abandoned. In this case, the switches may be magnetically latched by driving the cores momentarily to saturation, and subsequently released by demagnetizing the cores. Alternatively, the cores may be of a soft magnetic material, in which case latching may be accomplished, if desired, electrically by keeping the coils energized for the desired latching periods.

DETAILED DESCRIPTION A representative embodiment of the invention will now be described in connection with the accompanying drawing, wherein:

FIG. I is a schematic diagram of a portion of a crossbar switch according to the invention, showing the scheme of operation;

FIG. 2 is a plan view, partly schematic in form, with parts broken away and the actuators removed, of a crossbar switch according to a presently preferred embodiment of the invention;

PK]. 3 is a fragmentary cross-sectional view on an enlarged scale of the crossbar switch shown in FIG. I; and

FIG. 4 is a horizontal sectional view taken along the line 4-4 of FIG. 3.

As shown, a crossbar switch according to the invention includes a deck of four printed circuit cards 10, ll, 12, and 13, respectively, which carry the X and Y conductors l6 and 17, respectively, separated and shielded by three ground planes 20, 2], and 22. The first (top) printed circuit card 10 carries the top ground plane 20. The first array of conductors, referred to here as the Y conductors l7, lies between the first card 10 and the second card 11, The second, or middle ground plane 21 is between the second card 11 and the third card 12. The crossing, or X conductors 16 are between the third card 12 and the fourth card 13. The bottom ground plane 22 is secured to the bottom of the fourth card 13. The entire laminated structure is preferably reinforced and potted as desired in view of its intended final use. For clarity, reinforcing devices and the potting arrangement are omitted from the drawing.

Holes, not separately designated, extend through the deck of cards 10-13 and are lined with electrically conductive material as by electroplating with copper, for example. This may be done after the cards are cemented together to form the tightly laminated deck. Apertures 24 are provided in the ground planes 20, 21, and 22 around all of the holes that are aligned to provide contacts with the X and Y conductors l6 and 17. Other ones of the holes along the edges of the cards 10-13 are provided to connect the switch to an external circuit and to establish ground connections between the various planes of conductors.

The thicknesses of the cards l0-l3 and the thicknesses and widths of the X and Y conductors l6 and 17 are selected on the basis of known strip line theory for the desired transmission characteristics including impedance so that each one of the X and Y conductors l6 and 17 taken with the two ground planes 2022 on each side of it has the electrical characteristics ofa high frequency transmission line.

Pins 26 and 28, respectively, are fitted in the holes and extend through the deck for making the desired connections between the various planes of conductors and for connecting the X and Y conductors l6 and 17 to reed switches 30, which are mounted in U-shaped lugs 32 molded as integral parts at the upper ends of the pins 26. The pins 28 along the outer edges of the deck are shaped to fit connectors of any desired type for connecting the crossbar switch to an external circuit.

The arrangement of the X and Y conductors l6 and I7 and their connections to respective ones of the pins 26 is largely a matter of design. In general, the Y conductors 17 extend at right angles to the X conductors l6, and if laterally extending branches are needed to connect them to desired ones of the pins 26, the branches are made as short as possible to minimize their effect on the transmission line characteristics of the conductors l6 and 17. As shown, the crossbar switch is arranged for a single switched connection at each cross-point, it is a simple expedient, however, to add X conductors l6 and Y conductors 17 to provide for two, three, or more connections at each cross-point. In such case, the layout should be made so that all of the reed switches at each cross-point lie closely adjacent to each other so that they may be actuated by a single actuator.

Another printed circuit card 34 called the actuator board is mounted above the top of the crossbar deck, spaced from it by spacer blocks (not shown) for carrying the actuators 40 for the reed switches 30. As best shown in F163, each of the actuators includes an H-shaped core 42 encased within a split bobbin 44. A coil 46 is wound on the bobbin 44 along the central connecting bar of the H, and preferably covered with a sheet 47 of highly permeable material such as mu-metal. Pole pieces 48 and 49, and 50 and 51 extend from the outer ends of the legs of the H-shaped core 42 inwardly generally parallel with the central bar portion of the H to about the middle thereof. The reed switches 30 mounted on the crossbar deck lie between the pole pieces 48 and 49 at the lower ends of the H-core 42. The actuators 40 are fixed to the actuator board 34 by any desired means, The upper legs of the H-cores extend through the actuator board, and auxiliary reed switches 52 are mounted on top of the actuator board 34 between the upper pole pieces 50 and 51 to provide supervisory signals. The ac tuator board 34 is suitably apertured to facilitate assembly of the actuators on it and may carry printed circuits on both sides for establishing connections between terminals along the edges of the board 34 and the terminals of the coils 46 and of the supervisory reed switches 52.

If electrical latching is provided, circuit components such as integrated circuit flip-flops (not shown) may also be mounted on the actuator board 34. Magnetic latching, however, is provided in accordance with the preferred embodiment of the invention, as hereinabove noted, and, therefore, in the preferred form, auxiliary circuit components need not appear on the actuator board 34.

The pole pieces 48 and 49, and 50 and 51 serve to concentrate the magnetic field strongly in the region of the contact points of the reed switches 30 and 52, thereby to insure maximum contact pressure. The arrangement makes actuation of the reed switches relatively insensitive to displacement of the reed switches from their design positions centered between the two pole pieces 48 and 49, and 50 and 51 of each pair. This permits a large manufacturing tolerance in the assembly because, for example, the contact pressure for any one of the reed switches 30 does not vary appreciably so long as it remains in the air gap between the pole pieces 48 and 49, whether it be closer to the first pole piece 48 or to the second pole piece 49, or equally spaced between them. In addition, the pole pieces 48-5] act as magnetic shields to immunize the reed switches 30, 52, and 53 from undesired closure due to stray magnetic fields. The reed switches may thus be arranged in a very compact array without the need for special shields to prevent magnetic cross coupling between cross-points.

Positive closure by a common actuator is also achieved for all of several juxtaposed reed switches because the reed switches do not shunt the airgap but are magnetically in series in it. In the usual arrangement heretofore employed, the reed switches have been placed generally parallel with the main axis of the actuating coils in shunt with each other in the magnetic gap. When the coils were energized, closing of successive reed switches reduced the fiux in the gap, with the result that at times not enough flux was available to insure closure of all of the reed switches. In the present arrangement, by contrast, the reed switches are in series transversely across the main flux path between the ends of the pole pieces, and the effect of closure of the first reed switch does not reduce, but slightly enhances the flux applied to the successive reed switches.

What we claim is:

I. A crossbar switch comprising a deck of printed circuit cards carrying X and Y conductors in strip-line form, an array of reed switches on an outer surface of said deck for selectively connecting respective ones of said X conductors to respective ones of said Y conductors, said deck having apertures extending through it and lined with conductive material for electrically connecting said X and Y conductors to points on the outer surface of said deck, pins fitted in said apertures for mounting and electrically connecting said reed switches to said conductive material, and magnetic actuators mounted adjacent to said reed switches for selectively actuating them.

2, A crossbar switch according to claim 1, wherein said switches are aligned in parallel array, and said actuators are aligned parallel with said switches and include pole pieces of magnetically permeable material extending along opposite sides of said switches and terminating adjacent to the midpoints therealong, said pole pieces serving to concentrate the flux developed by said actuators near the contact tip portions of the reeds of said switches and also to shield said switches against stray fields.

3. A crossbar switch according to claim 4 including an auxiliary printed circuit board, electromagnetic actuators mounted on said auxiliary board for actuating said reed switches, means for mounting said auxiliary board in fixed spaced relation to said deck of cards, each of said actuators having a magnetic core of H-shaped longitudinal section and an energizing coil carried by the central bar portion of said core, the outer legs of each core defining two magnetic airgaps, one of said gaps being positioned along one of said reed switches and the other of said gaps lying on the opposite side of the central bar portion of the core from said one gap, and an auxiliary reed switch mounted on said auxiliary board in said other one of said gaps. 

1. A crossbar switch comprising a deck of printed circuit cards carrying X and Y conductors in strip-line form, an array of reed switches on an outer surface of said deck for selectively connecting respective ones of said X conductors to respective ones of said Y conductors, said deck having apertures extending through it and lined with conductive material for electrically connecting said X and Y conductors to points on the outer surface of said deck, pins fitted in said apertures for mounting and electrically connecting said reed switches to said conductive material, and magnetic actuators mounted adjacent to said reed switches for selectively actuating them.
 2. A crossbar switch according to claim 1, wherein said switches are aligned in parallel array, and said actuators are aligned parallel with said switches and include pole pieces of magnetically permeable material extending along opposite sides of said switches and terminating adjacent to the midpoints therealong, said pole pieces serving to concentrate the flux developed by said actuators near the contact tip portions of the reeds of said switches and also to shield said switches against stray fields.
 3. A crossbar switch according to claim 4 including an auxiliary printed circuit board, electromagnetic actuators mounted on said auxiliary board for actuating said reed switches, means for mounting said auxiliary board in fixed spaced relation to said deck of cards, each of said actuators having a magnetic core of H-shaped longitudinal section and an energizing coil carried by the central bar portion of said core, the outer legs of each core defining two magnetic airgaps, one of said gaps being positioned along one of said reed switches and the other of said gaps lying on the opposite side of the central bar portion of the core from said one gap, and an auxiliary reed switch mounted on said auxiliary board in said other one of said gaps. 